Please tell me it might not be head gasket

It's better to remove the O-ring from the coolant bottle cap. That'll prevent the cooling system from pressurizing and limit the amount of coolant being dumped into the combustion chamber.

ANY sealer you put into your cooling system is going to clog it - so even if you do fix the head gasket, your cooling system will be compromised and will need replacement. Quick fix NOW for expensive repairs later; if it works and it's ONLY temporary.

Your car, your choice.....

 

Likely the head was machined, not the block....